Decentered optical system, image projection apparatus incorporating a decentered optical system, and imaging apparatus incorporating a decentered optical system

A decentered optical system, comprising:

• a first optical element comprising at least three, mutually decentered optical surfaces including a first surface through which light can transmit, a second surface through which light can transmit and which is capable of internal reflection, and a third surface through which light can transmit and which is capable of internal reflection, wherein said first optical element is filled inside with a medium having a refractive index greater than 1, and at least one of the three optical surfaces has a rotationally asymmetric configuration, and
• a second optical element located on a second surface side of said first optical element and comprising at least two, mutually decentered optical surfaces including a first surface through which light can transmit and a second surface through which light can transmit and which has an outwardly concave configuration, wherein said second optical element is filled inside with a medium having a refractive index greater than 1, and at least one of said two optical surfaces has a rotationally asymmetric configuration, wherein:
• said first optical element and said second optical element are spaced away from each other in an effective area through which a light beam passes, and satisfy the following condition (1):
• 0<DMAX/f≦0.3 (1)
• where DMAX is a maximum value of a distance as measured in said effective area through which said light beam passes on a section including a center chief ray of said light beam in a direction parallel with said center chief ray between the second surface of said first optical element and the first surface of said second optical element, and f is a focal length of said decentered optical system.